Springs



UNITED STATES PATENT OFFICE.

MIDDLETON CRAWFORD, OF COLORADO SPRINGS, COLORADO, ASslGNOR OF THREE-FOURTHS TO THOMAS C. PARRISH AND DUNCAN CHISHOLM, OF SAME PLACE, AND JAMES POURTALES, OF SILESIA, GERMANY.

PROCESS OF EXTRACTING PRECIOUS METALS FROM THEIR ORES.

SPECIFICATION forming part of Letters Patent No. 543,676, dated July 30, 1895.

Application filed January 8, 1895. Serial No. 534,223. (N pecimens.)

To all whom it may concern:

Be it known that I, MIDDLETON CRAWFORD, a subject of the Queen of Great Britain, (but having declared my intention of becoming a citizen of the United States,) residing at Colo rado Springs, in the State of Colorado, have invented certain new and useful Improvements in the Process of Extracting Precious Metals from their Ores, (Case E,) whereof the [0 following is a specification.

My invention relates to an improved process for the extraction and recovery of precious metals from their ores by means of the solvent action upon said metals of the salts I5 of cyanogen-salts, commonly known as the cyanide process.

Generally speaking, the cyanide process consists, first, in lixiviating the pulverized ores with a solution of cyanide of potassium or other similar salt, the result being the formation from a portion of the gold and silver or other precious metal of a soluble aurocyanide of potassium or other corresponding salt, which is taken up inthe solution; and,

2 5 second,in separating the precious metals from this solution either by electrolysis or by passing the solution over zinc plates or shavings, whereby the precious metals are precipitated, or by other appropriate means. This pro- 0 cess has hitherto usually been applied to what are termed tailings-that is, to gangue which has been already treated by an amalgamatin g process--the amalgamatin g process, as is well known, being very efficient for the 5 removal of the larger particles of gold, but

always failing more or less to remove the microscopic or float gold or the gold contained in concentrates, which latter forms are particularly amenable to the cyanide process.

Myinvention relates, especially, to the first step in the cyanide process and in the preliminaries thereto.

The chief difficulties hitherto incurred in the cyanide process have resulted from the great length of time required to fully dissolve the precious metal in the cyanide solution, requiring, as ordinarily practiced, many days. I add to the solution of cyanide of potassium, prior to its employment in the lixiviating 5o process, certain substances by means of which the rate at which the dissolution of the gold or silver is accomplished is greatly facilitated and the quantity capable of being dissolved greatly increased, thereby avoiding this delay. 5 5

It has been recognized hitherto that the solution of gold in cyanide of potassium and the consequent formation of an aurocyanide requires the presence of oxygen, the formula by which this reaction takes place being expressed as follows:

and methods have been experimented with in order to supply this extra molecule of oxy- 6.5 gen, but without practical results, the difliculties experienced being twofold: First, the excess of oxygen has been found to be in such unstable combination with the liquid as to be lost almost as rapidly as put into it, or, at least, before it can be made practically available for the purpose of taking up the gold, thus rendering it impossible to use the solution for anything like a continuous process; and, second, the substances which 75 have been added to the cyanide solution for the purpose of thus imparting to it an excess of oxygen have been accompanied by greater or less quantities either on the one hand of acid or on the other hand of alkali, both of which are highly detrimental to, if they do not substantially prevent, the proper carrying out of the process, for the reason, first, that either an acid or alkaline excess in the solution tends to oxidize any base metals 85 which may be present in the ore, so that the cyanide attacks them in preference to the gold, and, secondly, because an excess of acid has a tendency to effect the direct decomposition of the cyanide, throwing 0E hydrocy- 9o anic acid.

The chemical substance which I have discovered, and the preparation of which I am now about to describe, when added to the cyanide solution imparts to it an excess of oxy- 5 gen, but is as nearly as possible free from either excess of acid or excess of alkali-that is to say,'almost neutralas a result of which the cyanide solution is rendered capable of dissolving a much larger amount of precious mo metal, to the entire exclusion of base metal, and in a much shorter time than has hitherto been practicable by the means formerly employed. The chemical substance which possesses these qualifications is prepared as follows:

Iagitate ether with binoxide of barium and add thereto gradually small quantities of very dilute hydrochloric acid. The precipitated chloride of barium is removed, and subsequently any small traces of acid neutralized by adding silicate of soda or other suitable salt. The resultant solution is chemically peroxide of hydrogen; but it differs from the ordinary commercial article in that it is sufficiently stable to answer the purposes of my process, and also in being free from the objectionable acid excess, which is invariably present in peroxide of hydrogen when prepared in the ordinary way, which by its presence both tends to decompose the cyanide and also the base metal in the ore. With the lixiviating solution thus formed the powdered ore contained in the precious metals is lixiviated, and if necessary agitated. If the ore is itself found to be either alkaline or acid it should be neutralized prior to the addition of the lixiviating solution. Although under or dinary circumstances, and in accordance with the methods heretofore employed, the agitation of pulverized ore with a cyanide solution requires to be carried on many days before the dissolution of the precious metal is sufticiently complete, I find that by reason of the addition to the cyanide solution of the substance which I have described, I am enabled to so facilitate the lixiviating process that it occupies but about an hour. When the lixiviating process has proceeded for the requisite length oftime,the gangue and also the solution are withdrawn from the lixiviating vessel, and if the ore which is being treated has contained comparatively coarse particles of the metal, (which particles are incapable of solution by a cyanide process, under any circumstances, within any reasonable time,) the gangue with its accompanying solution are passed through an amalgamating process whereby this coarse gold may be reclaimed,which proeess,in case electrical amalgamation is employed, extracts a certain portion of the dissolved metal also from the solution by precipitation. The tailings are then separated from the solution by any suitable process and the solution treated electrolytically until the dissolved gold is separated therefrom. Other well-known methods of separation may be employed, if desired. The residuum of the cyanide solution may then be run back, preferably through rubber pipes, to the tank in which it was originally treated and used over again, making the process continuous. I find that by reason of the addition to the cyanide solution of the substance which I have described, its tendency to deteriorate is very much decreased, making it thereby possible to continue to use the same solution for a much greater length of time than would otherwise be the case.

The advantages of this process are obvious. The comparatively short time required for the lixiviating process enables the ore to be rapidly run through, so that the quantity of ore which may be treated by a given amount of cyanide is very largely increased. This renders it practicable to apply the cyanide process not simply to tailings, as has heretofore been done, but to the ore as it comes from the mine, and by combining it with an amalgamating process in the order I havcdescribedthat is to say, passing the gangue over the mercury subsequent to its lixiviating with the cyanide-I [ind that by means of what is practically one continuous process I am able to extract alarger proportion of precious metal from the ore than has hitherto been done by the use of two separate processes.

Having thus described my invention, I claim- The improved process of extracting precious metals from their ores which consists in, first, lixiviating the ore with a cyanide solution to which has been added a small quantity of a substance prepared by agitating ether with binoxide of barium and adding thereto small quantities of very dilute hydrochloric acid, and neutralizing by silicate of soda; and, second, separating the precious metal from this solution in which the ore has been lixiviated, substantially as described.

MIDDLETON CRAWFORD. [1,, s] Witnesses:

GEORGE S. ELSTUN, HENRY L. B. WILLS. 

